Which units are most effective at destroying buildings?

Solution 1:

For the Banished, the Locust unit is specifically for destroying buildings. A bunch of these against a building should take it down pretty fast.

As for the USMC, I don't think there is an actual unit specifically for targeting buildings. However, Scorpions are probably the best at taking out buildings, or Grizzly Tanks if playing as Sgt. Forge. Upgrading the Scorpion tanks to have their Canister Shell ability makes them pretty devastating against buildings, especially when you have multiple tanks fire all at one time at a building. Marines when upgraded to have rocket launchers make them pretty effective at this as well, but you need a lot of them focused on a building at a time.

The Vulture unit is very strong as well, but due to the amount of man power it takes to create one, it makes it difficult to get multiples of them.